Transmission and brake for stopping conveyors

ABSTRACT

A drive shaft of an intermittently movable conveyor is alternately entrainable, via respective slipping clutches, by a high-speed and a low-speed input shaft, the switchover to low speed occuring shortly before the arresting of the drive shaft at the end of an operating cycle. A pulse counter excited by the drive shaft measures a braking interval in the final phase of each operating cycle and, at the inception of that interval, triggers a generator of progressively increasing voltage whose output causes the switchover upon reaching a reference value registered in a storage circuit. Depending upon the length of time required for the drive shaft speed to reach its lower limit, the stored reference voltage is either increased or reduced to delay or advance the switchover point to a predetermined instant slightly preceding the end of the cycle.

United States Patent [72] Inventors Rudolf Wanner Aystetten; BertholdMader; Theodor Mayr, both of Augsburg, all of Germany [211 App]. No.873,944 [22] Filed Nov. 4, 1969 [45] Patented Jan. 11, 1972 [73]Assignee Firma Bowe, Bohler 8; Weber KG.

Maschinenfabrik Augsburg, Germany [32] Priority Nov. 6, 1968 [3 3]Germany [31] P18073643 [54] TRANSMISSION AND BRAKE FOR STOPPINGCONVEYORS 7 Claims, 2 Drawing Figs.

[52] US. Cl 192/146, 192/9, 192/142 R, 198/1 10,317/140 [51] lnt.Cl F16h57/10 [50] Field of Search 192/9, 145, 146, 148, 142 R; 198/1 10MAGNETIC SLIPPING cLufCHES 1 FLIP/116R Primary ExaminerBenjamin W. WycheAnorneyKarl F. Ross ABSTRACT: A drive shaft of an intermittently movableconveyor is alternately entrainable, via respective slipping clutches,by a high-speed and a low-speed input shaft, the switchover to low speedoccuring shortly before the arresting of the drive shaft at the end ofan operating cycle. A pulse counter excited by the drive shaft measuresa braking interval in the final phase of each operating cycle and, atthe inception of that interval, triggers a generator of progressivelyincreasing voltage whose output causes the switchover upon reaching areference value registered in a storage circuit. Depending upon thelength of time required for the drive shaft speed to reach its lowerlimit, the stored reference voltage is either increased or reduced todelay or advance the switchover point to a predetermined instantslightly preceding the end of the H cycle.

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Rudolf Wanner Bertha/d Mader Theodor Mayr INVENTORS.

3 WA (Ros Attorney TRANSMISSION AND BRAKE FOR STOPPING CONVEYORS Ourpresent invention relates to a system for intermittently driving a loadsuch as a movable machine part, e.g., a conveyor serving to feed anelongate web or a succession of sheets of paper or the like to a cutter,printer or other processing stage, in repetitive operating cycles eachincluding a highspeed phase and a low-speed phase.

In such a machine it is desirable to operate the conveyor or othermachine part at high speed over the major portion of a working cycle andto minimize the impact of stoppage by reducing this speed to a low leveljust before the machine part is arrested at the end of the cycle. Since,however, the duration of a cycle is subject to variations due to changesin supply voltage or frequency, wear of brake linings, thermal effectsand other factors, the instant of arrival of thy driven part in itslimiting position cannot be predicted with certainty. In practice, withutilization of conventional speed-control devices, the duration of anoperating cycle will be subject to relatively slow fluctuations which inthe past have necessitated on occasional manual resetting of thecontrols.

The general object of our present invention is to provide an improvedmethod of and means for so operating a machine of this type that theintermittently movable part thereof is always decelerated at a safedistance from its terminal position but so close to that position thatthe average operating speed remains high.

A more specific object is to provide a system of this characterparticularly adapted for the control of an intermittently andunidirectionally rotating drive shaft, e.g., as used to operate aconveyor of a paper-cutting machine.

In accordance with an important aspect of this invention, we measure apredetermined length of travel (e.g., in terms of revolutions of a driveshaft) for the driven member or the load, this length being somewhatless than the total displacement of the load during an operating cycle;the remainder of the cycle, or at least the major portion of theremainder, constitutes a braking interval during which the load speed isprogressively reduced from a relatively high level to a relatively lowlevel. At some point during this braking interval, as determined by thecomparison of a progressively changing variable (e.g., a voltage) with areference magnitude, the load is decelerated to a relatively low speedlevel, preferably by switching its drive from a high-speed input to alow-speed input; after the load has reached its lower speed level, theduration of its movement at that speed to its terminal position (or to aposition slightly preceding same) is ascertained and is used to increaseor decrease the reference magnitude so as to delay or advance the startof the slowdown in the next cycle in a manner maintaining the end of thedeceleration step close to the terminal position, i.e., keeping the timeof low-speed travel as short as possible.

If the load is represented by or coupled with a rotatable drive shaft,the length of travel at high speed to an intermediate point and at lowspeed to a terminal point may be conveniently measured with the aid ofpath-length-measuring means comprising a pulse counter excited by apulse generator driven by the shaft. The pulse counter, on reaching afirst count denoting the start of the braking interval, emits a signalwhich, according to a preferred embodiment, triggers speedsensing meansincluding a generator of a sawtooth voltage whose rising flank (ofeither polarity) progressively approaches a stored potential until acomparator indicates the equality of the two voltage levels. At thatmoment the drive shaft, heretofore coupled to a high-speed input shaftfor entrainment thereby, is decoupled from that input shaft and iscoupled through a slipping clutch to a low-speed input shaft so asgradually to approach the velocity of the latter. Generally, thisvelocity (or a critical velocity slightly higher than that of thelow-speed input shaft) is reached before the counter emits a secondsignal indicating the end of the braking interval; in this case, thedevice (e.g., a capacitance) storing the reference potential is furthercharged during the span between the end of deceleration and the end ofthe braking interval so that the magnitude of the reference potential isincreased. In the next operating cycle, therefore, the start ofdeceleration is delayed so as to foreshorten the time of low-speedtravel. If, however, the end of deceleration as determined by thecomparator output occurs at an instant beyond the braking interval(whose end, therefore, must precede the arrival of the load in itsterminal position), the storage device is partly discharged during theperiod between the end of the braking interval and the reduction of theshaft speed to the critical level so as to lower the reference potentialwhereby the start of deceleration is advanced in the following cycle.The rates of charge and discharge should be so chosen that the positiveor negative increment per cycle of the time elapsed between the start ofthe braking interval and the beginning of deceleration amounts to only afraction of that braking interval, the system being thus able tocompensate for gradual fluctuations in the length of an operating cyclewhile maintaining the end of deceleration close to the stopping point.

The above and other features of our present invention will now bedescribed in greater detail with reference to the accompanying drawingin which:

FIG. 1 is a somewhat diagrammatic layout of a control system accordingto the invention; and

FIG. 2 is a set of graphs relating to the operation of the system ofFIG. 1.

As illustrated in FIG. 1, a motor M representing a continuously operabledrive means drives via a transmission 1 a pair of shafts 2 and 3, shaft3 rotating at a high speed v whereas shaft 2 rotates at a considerablylower speed v Shafts 2 and 3 serve as alternate input members for adriven shaft 5 which can be selectively coupled to either of these inputshafts through a switching mechanism 4 including yieldable couplingmeans shown as a pair of slipping clutches which are altemately operableto accelerate the shaft 5 to speed level V and to decelerate it to speedlevel v A machine part to be intermittently advanced, here shown as aconveyor 6, is coupled with shaft 5 for entraining a workpiece 8, suchas a paper web, in the direction of an arrow 7. Conveyor 6 may be partof a paper-cutting machine having means for slicing the web 8 wheneverthe conveyor 6 comes to a halt. For this purpose, the conveyor can bepositively arrested by a solenoid 10 which drives a pawl 11 intoengagement with a ratchet 9 on shaft 5.

Also mounted on shaft 5 for rotation therewith is a toothed wheel 12moving in the field of a magnetic pickup head 13 which generates a pulseupon the passage of each tooth. These pulses are delivered to a counter14 having three outputs Bl, BG and VE. The pulses registered in counter14 are further transmitted to a sawtooth-wave generator 15 where theytrigger successive voltage cycles. A speed-sensing means constituted bya threshold sensor 16 compares the stepped voltage from generator 15with a fixed but preferably adjustable voltage level 17 (see FIG. 2)and, if the flank of any sawtooth rises to that level, energizes thesetting input of a bistable timing element or flip-flop 18 whose setoutput is fed to an input of an AND-gate 20 and in parallel therewith toan inverting input of another AND-gate 21. The second input of AND-gate20 is connected to the output BI of pulse counter 14, in parallel withan input of a further AND-gate 19 having an inverting second inputconnected to the set output of another flip-flop 23. The second input ofAND-gate 21 is connected to the output B0 of pulse counter 14 whoseoutput VE drives the resetting input of flip-flop 23 and, in paralleltherewith, the solenoid 10.

The outputs of coincidence gates 20 and 21 are tied to a charging inputand a discharging input respectively, of a storage device C which mayinclude a conventional resistance/capacitance network. These two inputs,when energized, cause a gradual and preferably linear change in theoutput voltage of device C which remains constant if neither of theseinputs is energized. A further input 29 serves for a rapid resetting ofthe device C to zero when manually connected to a voltage source notshown. Charging and discharging along slightly nonlineare.g.,exponentialcharacteristics may be tolerated.

Another sawtooth-voltage generator H is triggerable by an output signalfrom AND-gate 19 to produce a rising voltage, here assumed to bepositive, and to return to zero whenever the input signal disappears.The outputs of generator H and storage device C are applied to oppositeinputs of a comparator 22 which delivers an output signal to the settinginput of flip-flop 23 as soon as the generator voltage reaches theoutput potential of unit C. The set output of flip-flop 23, aside frombeing fed to the inverting input of AND-gate 19 as described above, isalso transmitted to the resetting input of flip-flop 18 and to a relay24 which, when energized, actuates switchover means in the form of asolenoid 25 for reversing the switching mechanism 4 as diagrammaticallyindicated by an arrow 26.

The operation of the system shown in FIG. 1 will be .described withreference to FIG. 2 which shows in graph (a) the velocity v of shaft andin graph (b) the voltages V in the outputs of circuits 14, H and C, allplotted against time t in the course of a complete operating cycle ofthe system.

For the sake of simplicity it will be assumed that the cycle starts at atime 1,, with shaft 4 rotating at speed v,, although in practice it willrequire a certain length of time to bring this shaft up to the speed ofinput shaft 3 upon the throwing of switching mechanism 4 into itshigh-speed position. The rotation of shaft 5 causes the impulsegenerator I2, 13, forming part of the path-length-measuring meanscontrolled by this shaft, to produce a train of counting pulses Pfollowing one another in rapid succession when the shaft speed is high.Generator thus produces a train of sawtooth pulses SP of high frequencybut low amplitude, well below the threshold 17 of sensor 16.

Since the cadence of pulses P is proportional to the rotary speed ofshaft 5 and therefore to the length of travel of conveyor 6, theattainment of a predetermined pulse count P signifies the arrival of theload (i.e., web 8) in a predetermined position close enough to the limitof its stroke to allow deceleration of shaft 5 to begin. This pulsecount P occurs at a time t whose distance from starting time 1, may besubject to variation. Time t marks the beginning of a braking intervalcharacterized by the presence of a first signal voltage on counteroutput B], as illustrated in FIG. 2(b), during which the switchover fromhigh speed v, to a critical speed V, (slightly exceeding the level v,)starts at a time t, and ends at a time t The braking interval terminatesat a time t, with energization of counter output 86 by a second signalvoltage upon the attainment of a pulse count P. Shortly thereafter, at atime 1,, counter output VB is briefly energized upon the occurrence of acount P' to actuate the solenoid 10 so that shaft 5 is arrested and thecycle ends.

The time interval T between instants t and 1, depends on the chargestored in circuit C, i.e., on the voltage level V applied to theright-hand input of comparator 22. The voltage V concurrently applied tothe left-hand input of this comparator constitutes a progressivelychanging variable which rises from zero at instant t and reaches thelevel V at instant t, to start a time interval T, during which thedeceleration of shaft 5 takes place. Thus, the output of comparator 22sets the flip-flop 23 with consequent blocking of AND-gate 19 to restorethe sawtooth generator H to zero, resetting of flip-flop l8 andenergization of relay 24 to shift the mechanical switch 25.

As the shaft speed 27 decreases as shown in FIG. 2(a), the spacing ofcounting pulses P increases, as does the amplitude of sawtooth steps SP.Finally, at time 1,, threshold sensor 16 responds and sets the flip-flop18 whereby AND-gate 20 is unblocked in view of the presence of voltagefrom counter output BI on its other input. This action charges thestorage device C to raise its output voltage to a new level V during aninterval T, ending at instant t i.e., with the deenergization ofcounter-output BI. Since flip-flop I8 is set, the energization of-output80 has no effect upon the blocked AND-gate 21 and does not cause anychange in the charge stored in device C.

After the energization of output VE has reset the flip-flop 23 andarrested the shaft 5 against the driving torque of shaft 2 transmittedto it through one of the slipping clutches in coupling 4, a new cycle isbegun with self-restoration of counter 14 to zero so that shaft 5 ispromptly released by the deenergization of solenoid I0 even as flip-flop23 returns the coupling mechanism 4 to its high-speed position. In thisnew cycle, the increased level of reference voltage V, causes a delay ofinstant I, marking the start of deceleration interval T,. This, in turn,reduces the length of time T, T, during which the conveyor 6 operates atlow speed.

If storage circuit C overcharges so that deceleration terminates at aninstant 1, within the final period T, as indicated at 28 in FIG. 2(a), aflip-flop I8 is not set during the braking interval characterized by theenergization of output BI so that AND-gate 21 is opened by theappearance of voltage on output 86 and causes a partial discharge of thestorage device C whereby the output voltage thereof is lowered asindicated at V in FIG. 2(x). Thus, the system tends to maintain the endof the deceleration interval T, close to the instant t, which coincideswith a load position just ahead of the terminal position of its stroke.

If the speed of motor M is changed, the storage circuit C may bedischarged via its reset input 29 in order to find its new levelconsistent with the altered operating conditions. In the first cyclefollowing such discharge, comparator 22 responds immediately to therising output voltage of generator H so that the braking interval startssubstantially at time t It will be noted that this braking interval hasbeen chosen considerably larger than the time T, required fordeceleration and that the rate of change of AV or AV" of referencepotential V from one cycle to the other, is relatively small so that theshift AT of the deceleration period from its initial position at thebeginning of the braking interval toward its ultimate position at theend of that interval will normally occur over a succession of severalcycles. This guards against overreaction to changing operatingconditions which might endanger the safety of operation.

With a total path length of, say, ll cm., and with an assumed speedratio of v,:v =l0: l the final slow-motion period T, would consumealmost half the time available for an entire cycle if the travel pathafter deceleration were 1 cm. With the present improvement, this finalstroke section and the time allotted to it may be considerably reduced,possibly to a value of zero or near-zero.

We claim:

1. A system for intermittently driving a load in repetitive operatingcycles, comprising:

a driven member connected with the load to be driven;

continuously operable drive means switchable between a high and a lowspeed level, said drive means being operatively connected with saiddriven member and including a yieldable coupling effective at least atsaid low speed level whereby said driven member is progressivelydecelerated upon a switching to said low speed level and is arrestableon being entrained at low speed;

switchover means for said drive means having a high-speed and alow-speed position;

path-length-measuring means responsive to the displacement of saiddriven member for emitting a first signal upon the attainment of apredetermined intennediate point of a working stroke and for emitting asecond signal upon the approach of a terminal point of said workingstroke;

generator means effective in the high-speed position of said switchovermeans and controlled by said path-lengthmeasuring means for starting thegeneration of a progressively changing variable upon the occurrence ofsaid first signal;

a source of a reference magnitude for said variable;

comparator means connected to said generator means and to said sourcefor determining the arrival of said variable at a value bearing apredetermined relationship with said reference magnitude, saidcomparator means on ascertaining said relationship providing an outputsignal controlling said switchover means for changing same to saidlow-speed position whereby said driven member is subjected toprogressive deceleration;

speed-sensing means controlled by said driven member for determining thearrival thereof at a critical speed close to said low speed level;

timing means jointly controlled by said speed-sensing means and saidpath-length-measuring means for determining the relative time positionof the instant of arrival at said critical speed and the emission ofsaid second signal, said source being responsive to said timing meansfor altering said reference magnitude in a sense shifting the point ofchange of said switchover means during a subsequent operating cycle toterminate the deceleration of said driven member at an instant closer tothe emission of said second signal;

and stop means controlled by said path-length-measuring means formomentarily arresting said driven member upon its arrival at saidterminal point and for restoring said switchover means to saidhigh-speed position.

2. A system as defined in claim 1 wherein said path-lengthmeasuringmeans comprises a pulse generator and a pulse counter receiving theoutput of said pulse generator.

3. A system as defined in claim 2 wherein said driven member is a shaft,said pulse generator including a toothed wheel on said shaft andelectromagnetic pick up means adjacent said wheel.

4. A system as defined in claim 2 wherein said speed-sensing meanscomprises a sawtooth-voltage generator triggerable by the output of saidpulse generator and threshold means for comparing the output of saidsawtooth-voltage generator with a predetermined amplitude level.

5. A system as defined in claim 1 wherein said generator means comprisesa voltage generator with a substantially linearly varying outputvoltage, said source being a storage circuit for an electrical charge.

6. A system as defined in claim 5 wherein said timing means comprises abistable element settable by said speed-sensing means and resettable bysaid comparator means, a first coincidence circuit jointly controlled bysaid bistable element and said path-length-measuring means for causing aprogressive increase in the charge of said storage circuit during aperiod beginning with said output signal and ending with said secondsignal, upon said output signal preceding said second signal, and asecond coincidence circuit jointly controlled by said bistable elementand by said path-length-measuring means for causing a progressivedecrease in said charge during a period beginning with said secondsignal and ending with said output signal, upon said second signalpreceding said output signal.

7. A system as defined in claim 6 wherein said first and secondcoincidence circuits comprise a pair of AND-gates with respective inputsconnected in parallel to an output of said bistable element, one of saidinputs including an inverter.

1. A system for intermittently driving a load in repetitive operatingcycles, comprising: a driven member connected with the load to bedriven; continuously operable drive means switchable between a high anda low speed level, said drive means being operatively connected withsaid driven member and including a yieldable coupling effective at leastat said low speed level whereby said driven member is progressivelydecelerated upon a switching to said low speed level and is arrestableon being entrained at low speed; switchover means for said drive meanshaving a high-speed and a low-speed position; path-length-measuringmeans responsive to the displacement of said driven member for emittinga first signal upon the attainment of a predetermined intermediate pointof a working stroke and for emitting a second signal upon the approachof a terminal point of said working stroke; generator means effective inthe high-speed position of said switchover means and controlled by saidpath-length-measuring means for starting the generation of aprogressively changing variable upon the occurrence of said firstsignal; a source of a reference magnitude for said variable; comparatormeans connected to said generator means and to said source fordetermining the arrival of said variable at a value bearing apredetermined relationship with said reference magnitude, saidcomparator means on ascertaining said relationship providing an outputsignal controlling said switchover means for changing same to saidlow-speed position whereby said driven member is subjected toprogressive deceleration; speed-sensing means controlled by said drivenmember for determining the arrival thereof at a critical speed close tosaid low speed level; timing means jointly controlled by saidspeed-sensing means and said path-length-measuring means for determiningthe relative time position of the instant of arrival at said criticalspeed and the emission of said second signal, said source beingresponsive to said timing means for altering said reference magnitude ina sense shifting the point of change of said switchover means during asubsequent operating cycle to terminate the deceleration of said drivenmember at an instant closer to the emission of said second signal; andstop means controlled by said path-length-measuring means formomentarily arresting said drIven member upon its arrival at saidterminal point and for restoring said switchover means to saidhigh-speed position.
 2. A system as defined in claim 1 wherein saidpath-length-measuring means comprises a pulse generator and a pulsecounter receiving the output of said pulse generator.
 3. A system asdefined in claim 2 wherein said driven member is a shaft, said pulsegenerator including a toothed wheel on said shaft and electromagneticpick up means adjacent said wheel.
 4. A system as defined in claim 2wherein said speed-sensing means comprises a sawtooth-voltage generatortriggerable by the output of said pulse generator and threshold meansfor comparing the output of said sawtooth-voltage generator with apredetermined amplitude level.
 5. A system as defined in claim 1 whereinsaid generator means comprises a voltage generator with a substantiallylinearly varying output voltage, said source being a storage circuit foran electrical charge.
 6. A system as defined in claim 5 wherein saidtiming means comprises a bistable element settable by said speed-sensingmeans and resettable by said comparator means, a first coincidencecircuit jointly controlled by said bistable element and saidpath-length-measuring means for causing a progressive increase in thecharge of said storage circuit during a period beginning with saidoutput signal and ending with said second signal, upon said outputsignal preceding said second signal, and a second coincidence circuitjointly controlled by said bistable element and by saidpath-length-measuring means for causing a progressive decrease in saidcharge during a period beginning with said second signal and ending withsaid output signal, upon said second signal preceding said outputsignal.
 7. A system as defined in claim 6 wherein said first and secondcoincidence circuits comprise a pair of AND-gates with respective inputsconnected in parallel to an output of said bistable element, one of saidinputs including an inverter.